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grandpasmokey
09-14-2013, 4:50 PM
I've tried to find info on this topic on Calguns and other internet sources but have struck out I'm sure someone here knows the answer.

I'm building my first AR10 (DPMS) and I'm researching barrels. I came across reference to the breech cone. What is this and what does it do? Thanks everyone.

As the build progresses, I will include pictures.

Gunsmith Dan
09-14-2013, 5:16 PM
Ahhh unless I am missing something are you talking about the a coned breech??

A coned breech for some rifles (mostly bolt actions) was part of the original design. Basically the breech face comes either flat 90 degrees, flat 90 degrees to the bore and recessed, angled "cone" cut inward toward the chamber bore hole or recessed with angled cone cut inward.

The main advantage to a coned breech is smoother closing/opening BUT the nose of the bolt face also needs to be coned forward at the same angle so there is a tight fit.

Someone can correct me if I am wrong but I have not heard to many semi auto rifles that are coned breech and really never heard of any AR platforms that are coned breech

grandpasmokey
09-14-2013, 6:48 PM
http://www.kriegerbarrels.com/AR_10DPMS_LR-c1246-wp3393.htm#AR-10/DPMS-LR

This page is from Kreiger Barrels. At the bottom of the page, under "AR10/DPMS" they refer to head spacing & proper breech cone. It seems to refer to the contour of the chamber. I think.

ar15barrels
09-14-2013, 9:28 PM
I'm building my first AR10 (DPMS) and I'm researching barrels. I came across reference to the breech cone. What is this and what does it do?

It helps get the cartridge into the chamber.

You can see it in the bottom half of the red circle in this photo:

http://farm3.static.flickr.com/2629/4039897556_1dddab0124_o.jpg

Gunsmith Dan
09-15-2013, 2:46 AM
Wow got to love it when manufacturers use wrong descriptions

This is a coned breech:

http://www.calguns.net/calgunforum/attachment.php?attachmentid=265246&stc=1&d=1379238637

The breech is the entire area not just around the bore.

What AR15Barrels showed you was a coned/beveled chamber or bore to improve feeding but in order to be a true coned breech that angle would have to be to the outer edge like the picture. The best example would be looking at original Springfield 1903 bolt action or the first Winchester M70 bolt action.

ar15barrels
09-15-2013, 11:10 AM
In reference to an AR type, the cone I posted above IS a slight breech cone though you could also call it a chamber-edge-chamfering.
I will agree that the AR type actions do not use a coned breaching system though as the front of the bolt is flat.
The chamber-edge-chamfer helps ensure that long pointy bullets make it into the chamber rather than stopping against the breech face.
Shorter bullets never touch the chamber-edge-chamfer as they are lifted up into the chamber by the feedramps on the back of the barrel extension.

BT JUSTICE
09-15-2013, 11:29 AM
Wow got to love it when manufacturers use wrong descriptions

This is a coned breech:

http://www.calguns.net/calgunforum/attachment.php?attachmentid=265246&stc=1&d=1379238637

The breech is the entire area not just around the bore.

What AR15Barrels showed you was a coned/beveled chamber or bore to improve feeding but in order to be a true coned breech that angle would have to be to the outer edge like the picture. The best example would be looking at original Springfield 1903 bolt action or the first Winchester M70 bolt action.

Wow! Any pictures of the bolt face that matches this cone?

swifty
09-15-2013, 11:43 AM
Wow! Any pictures of the bolt face that matches this cone?

M1917 Enfield and 1903 Springfield are cone breeched.

ar15barrels
09-15-2013, 12:08 PM
Wow! Any pictures of the bolt face that matches this cone?

http://www.bordenrifles.com/images/gsborden01.jpg

kendog4570
09-15-2013, 12:47 PM
It helps get the cartridge into the chamber.

You can see it in the bottom half of the red circle in this photo:

http://farm3.static.flickr.com/2629/4039897556_1dddab0124_o.jpg

The M16 barrel print calls this area the feed cone ( Drawing #8448548). I believe it is 61 degrees, but I cannot read my print very clearly. This is typical in the firearms industry, that there is little in the way of standardization of terminology or part names. I would bet that Krieger has a clear drawing of this and calls it correctly.
It would appear then a "breech cone" and a "coned breech" are two different things. One is a cut or location on the barrel, and the other is a breeching system.

If anyone has a clear copy of the above mentioned drawing I would love to get a copy.

ar15barrels
09-15-2013, 12:58 PM
It would appear then a "breech cone" and a "coned breech" are two different things.
One is a cut or location on the barrel, and the other is a breeching system.

That's how I see it too.